The invention relates to an apparatus and method for dispensing and weighing individual particulate material ingredients to be formed into a composite batch.
In the plastics industry, as well as in other industries, there is a need for mixing materials, including a large weight of base material and one or more relatively small weights of additive material. For example, it may be desired to provide four hundred pounds of base material and one or more additives, each having a weight of from two to eighty pounds. These materials are of a particulate nature, and may be in one or more degrees of fineness. Thus, these materials may be powders, grains, particles and even small chips. It has been found that the most facile way of storing and dispensing the weighed amounts of these additive materials is through utilization of batch weighers, and a pneumatic delivery conduit. Each batch weigher includes a storage hopper, a scale, some apparatus to deliver material from the storage hopper to the scale, and a branch conduit for delivering the weighed batch of material from the scale to the pneumatic delivery conduit.
In the plastics industry, in particular, it is highly critical that the final mass of material contains all of the ingredients prescribed, and, further, contains each of the ingredients in the prescribed amount. This is because the ingredients, themselves, are expensive, and the further processing of the ingredients into the desired plastic material or articles is also expensive, so that the processing of a mass which contains improper amounts of material is undesirably wasteful. As often happens, a mass of material, intended to be formed of a plurality of precisely weighed ingredients, is not actually composed of the ingredients in the amounts intended. This fact is not known, when the mass is to be subjected to further processing so that the mass of material is then processed, with the result that the final product must be either discarded, sold at a significant discount, or reprocessed, where possible, and in any event, these are expensive and wasteful additional steps which are undesirable.
In the practice which has existed with the equipment of the above described nature, where a mass of material has been mixed, and it is found that it contains an improper formulation of ingredients, that mass is, at some point in its processing, discarded, reprocessed or discounted, and a new mass is then produced, hopefully having the correct formulation.
Although the batch weighers and the pneumatic conveying systems which have been used are usually reliable, and usually there is delivery of the entire amount of the ingredient from each of the batch weighers to a collector, it is known that a deficiency arises in some instances, due to the failure of the material to be delivered by the pneumatic conveyor to the collector; some of the material, when a mal-function occurs, remains in a part of the system, such as in a separator for separating air from particulate material, which separator is in the system prior to the collector. In the past, there have been attempts to provide a solution to the problem of mal-function of the apparatus, particularly of the pneumatic conveyor and/or air-material separator, and this solution has been the provision of a material indicator placed in the base of the abovementioned separator, just above the air lock controlling the discharge of material from the separator, so as to detect any material remaining in the separator after it has been, in theory, exhausted of material. This solution has not been found to be satisfactory, because it is now recognized that the material indicator only gives an indication after several batches have passed through with resulting malfunctioning of each batch. That is, some of the material in each batch has failed to be discharged from the separator, and some of the material, of unknown constituency, has therefore remained in the separator. Thus, only after several, perhaps a dozen, batches have failed to be completely discharged from the separator into the collector is the operator made aware of the mal-function by the action of the material indicator.
In the distinct field of concrete mixing, Eirich et al U.S. Pat. No. 2,858,594 discloses a plant in which hoppers are provided for storing the various ingredients, the ingredients being delivered to mixers, and then to a final delivery hopper. In particular, a cement hopper is provided which deliver to a scale and sand and gravel containers are provided with screw conveyers which weigh out the components; however, this "weighing out" is imprecise, based on volumetric measurement. These screw conveyers deliver to a scale, and from the two scales, the sand, gravel and cement are delivered to a mixer, to which metered water is added. The ingredients are mixed, and then delivered to a feeder, the feeder including a scale, and the mixed components, i.e. concrete, are delivered by the feeder. Thus, the functions performed by the elements of this structure are of merely volumetric measurements, which are roughly, or grossly related to weight, but are, as noted, imprecise.